Dark matter has always been a tricky thing to nail down. It was first proposed to account for the discrepancy between the measured rotational behavior of galaxies and the rotation predicted by the combination of Newtonian gravity and the visible mass. Over time, it became clear that the normal matter, which interacts readily with light, accounts for less than 10 percent of the matter in the universe. The remaining matter could be inferred based on the dynamics of galaxies and larger structures, but could not be seen directly, and so picked up the name dark matter. Some scientists, however, have not been convinced that dark matter must exist, and suggested that we might have an incomplete understanding of gravity instead. It has been difficult to resolve this conflict, as dark matter doesn't interact with light, and its gravitational pull ensures that there's always regular matter associated with it, confusing efforts to detect it.

According to new observations, that last sentence should be rewritten to read "almost always." Using mutliple observations from a number of space-based astronomical platforms, a unique collision between two clusters of galaxies has been observed at a number of wavelengths. That collision, shown on the right, may be the most energetic event since the big bang. That image shows the galaxies of the cluster as the blue haze at the far edges, while gas glowing with X-rays shows up in red near the middle. Most of the visible mass is in the gas clouds, which have been moving slowly since the collision due to the energetic shock waves caused by the collision. The dark matter, however, shouldn't interact with this photon-based energy, and should therefore pass through the collision unhindered, winding up near the blue galaxy clusters.

The researchers scanned both the blue and red regions for gravitational lensing effects, which should be proportional to the matter present. The strongest lensing occurred at the galaxy clusters, rather than the gas. As a result, most of the matter must be with the galaxies, even though the majority of the visible matter is elsewhere, back in the gas clouds. In effect, the energy released by the collision caused visible and dark matter to separate, allowing the presence of dark matter to be detected separate from the normal association with visible matter. According to the scientists involved, there's no way to modify gravity to account for the dissociation of visible matter and gravitational attraction. Dark matter is the only possible explanation.

The paper describing these results is blunt in making this claim, as it's entitled, "A Direct Empirical Proof Of The Existence Of Dark Matter." The press conference was accompanied by a number of presentation graphics, including animations, which you can view here. This is a huge result; provided this interpretation holds up, this will be a rare moment in science, in that a single result should put to rest the dispute between two incompatible models. The scientific panel running the press conference are suggesting we can now stop arguing and focus on trying to determine what dark matter is made of.

The source link has all of the links to the various papers and whatnot, and is thus worth checking out if you like this type of thing. But yeah, that's pretty damn awesome.

Seriously though, I'll believe it when I see it replicated in a lab. Or, rather, don't see it.

I've said the same thing about G/god(s), and it never goes over that well. At least we now have direct evidence of dark matter acting to create a measurable phenomenon, so score one for physics, I guess.